I’m not really that knowledgeable about concept art, but I’d say this: your werewolf dude is pretty interesting - he is stylised and has character - but the other two are held back by technical problems.
I’d suggest looking at some photos of cars and jets for the second pic, and landscapes for the third, to get an idea of colour and tone. It looks like what you’ve done is decide what colour something’s going to be, then picked it out, then done some minor variations of light and dark there. That’s not how light behaves though. Even in settings with little colour variation, or bright backdrops, there is a lot more depth of colour, shadow and specular (shine) than you’ve put it.
See a shiny metallic surface here:
…or a matt surface here:
As for the desert, you’re not referencing real colours, so it ends up looking washed out and weak. See how even without strong lighting or brilliant sunsets desert stone has a much greater breadth of colour and value than in your image:
To paint without reference, you need to have a really good foundation in art, and usually even then it won’t look as good as if you had something to go from. So, always try to find some refs!
Hope this was helpful.